Plumbing Code Requirements: The following paragraphs provide several significant definitions and requirements involving installation of Air Gap Units and Indirect Drain Line Piping; specifically, when “water conditioning equipment” is to be installed in homes or buildings and connected to the potable water piping. The plumbing code information below is a paraphrased summary based on a review of several nationally recognized plumbing code manuals used in the United States.

The types of “water conditioning equipment” and appliances affected are automatic water softeners, back washable water filters, Reverse Osmosis (“RO”) drinking water systems, RO water coolers and other similar equipment—all of which, in order to function properly, are required to discharge liquid effluent via an indirect drain line to the building drainage system (drain piping). To prevent back siphonage and possible cross-connection, a proper air gap or listed air gap unit or listed air gap dispensing faucet is required by plumbing code to be installed downstream of the equipment in the indirect drain line piping. Depending on their design, our air gap units can be installed at the Indirect Liquid Waste Receptor or upstream at a suitable location in the indirect drain line piping.
Listed Air Gap Units:

We manufacture plumbing code listed Air Gap units in several sizes, models, mounting styles, and performance ranges, all of which are available with various inlet/outlet port connection details. When properly chosen to handle the “intended flow rate” and properly installed per their respective installation instructions; an air gap unit tested and accepted for plumbing code listing, provides the necessary back siphonage protection. Our air gap units are effective, economical, and easy to install.

All of our existing Air Gap units have recommended operating flow rates considerably less than their maximum possible flow rates. All units are durable molded plastic assemblies intended for cold water use and intended for easy mounting, easy connections, corrosion resistance, and long life. Plumbing codes require a minimum air gap spacing or air gap opening of 1 inch (or 25.4 mm), measured vertically. In compliance with these plumbing codes: all of our units offer air gap openings measured vertically of (1) inch or more and all units bear our trade name as well as the other required marking. All units have been patented and most have been trademarked. Depending on their particular installation, our air gaps offer the very best design and function. Furthermore, they all have backflow ratings at least as high as their recommended forward flow rating! (See backflow table).

The flowing back of used, contaminated, or polluted water from a plumbing fixture, receptor, or vessel into a potable water supply pipe due to a negative pressure (vacuum) in such pipe.


Any physical connection or arrangement between two otherwise separate piping systems, one of which contains potable water and the other water of unknown or questionable safety, whereby water may flow from one system to the other, the direction of flow depending on the pressure differential between the two systems. (Reference: Back-Siphonage)
Indirect Drain Pipe:

A pipe that does not connect directly with the drainage system but conveys liquid wastes by discharging through a physical air gap or listed air gap unit into a plumbing fixture or receptor which is directly connected to the drainage system.
Drainage Piping: Prohibited Fittings and Practices

…..”No band or saddle shall be used as a drainage fitting”……
“No drainage or vent piping shall be drilled for making connections thereto”…..
Indirect Liquid Waste Receptor:

A plumbing fixture designed specifically to collect and dispose of liquid waste from other plumbing fixtures, plumbing equipment, or appliances which are required to discharge to the drainage system through a physical air gap or listed air gap unit. The following are types of fixtures that commonly fall into the classification of acceptable indirect liquid waste receptors: floor sinks, mop receptors, service sinks, laundry tubs, and washing machine standpipe drains. Water closets of toilets in bathrooms are not acceptable as suitable indirect liquid waste receptors.
Important Installation Information:

No indirect liquid waste receptor shall be installed in any toilet room, closet, cupboard, or storeroom–indirect drain piping shall be easily accessible for flushing and cleaning from time to time, if necessary. When installed into the indirect drain line, the code required air gap or code listed air gap unit shall be readily accessible and visible and must be elevated higher than the piping extending downstream from the air gap. An air gap or air gap unit is not to be installed under a lid, behind an access panel, or locked door. The indirect drain line piping shall satisfy the air gap manufacturer installation instructions and be suitable in size and type to properly serve the connected upstream equipment.